Speicherung des labilen Silaethens Me2Si=C(SiMe3)2 mit Benzophenon [1] / Storing of the Labile Silaethene Me2Si = C(SiMe3)2 with Benzophenone [1]

Abstract

Benzophenone Ph2C=O is able to “store” the silaethene Me2Si=C(SiMe3)2 (1). produced from Me2SiX-CLi(SiMe3)2 (X = F. Br, Ph2PO4), under formation of a [2+4] cycloadduct (2b). At about 100 °C, 2b by way of 1 transfers into the [2+2] cycloadduct of 1 and Ph2C=O (3b), which in the course of transformation decomposes visibly (in the absence of Me3SiCl) or only by traces (in the presence of Me3SiCl) to secondary products. In the presence of ROH (R = H. Me. tBu. MeCO) or PhN = NSiMe3 or RN3 (R = tBu. Me3Si) or 2,3-dimethylbutadiene (dmb) about 100 °C 2b and 3b form by way of 1 insertion products of 1 into the OH bond of ROH or a [2+2] cycloadduct of 1 and PhN = NSiMe3 or [2 + 3] cycloadducts of 1 and RN3 or a [2+4] cycloadduct and an ene reaction product of 1 and dmb. The rate constants/half lives of the first order transformation of 2b into 3b or of the first order decomposition of 2b or of 3b in the presence of reactiv traps for 1 (ROH. Me3SiN3; benzene as solvent) are in the order of 0.3 × 10-4 s-1/τ1/2 = 7 h (2b→3b; 90 °C) 3 3×10-4 s-1/τ1/2 = 3/4 h (2b + traps; 90 °C), 0.4 × 10-4 s-1/τ1/2 = 5 h (3b + traps. 110 °C).